Metal boride films have been formed using various chemical vapor deposition (CVD) methods. In the CVD methods, gaseous source chemicals are introduced into a reaction space at the same time, resulting in a deposition of a metal film on the substrate. In order to thermally activate some of the gaseous source chemicals, the CVD methods tend to take place at temperatures as high as 1200° C. The high substrate temperatures relative to thermal budgets may be problematic, especially for state-of-the-art semiconductor fabrication processes such as metallization.
In addition, physical vapor deposition (PVD) methods have also been used to deposit metal borides. PVD methods generally deposit along a line-of-sight. However, line-of-sight deposition results in insufficient thin film coverage in certain areas where complex substrate contours are involved. Also, line-of-sight deposition results in low-volatility precursors depositing on the first solid surface encountered, leading to low-conformality coverage.
Atomic layer deposition (ALD) has been used to form metal carbide films. For example, U.S. Pat. No. 7,611,751 to Elers discloses methods for forming a metal carbide film through spatially and temporally separated vapor phase pulses of a metal source chemical, a reducing agent, and a carbon source chemical. Similarly, U.S. Pat. No. 8,841,182 to Chen et al. discloses the formation of titanium carbide films through an ALD process. However, no known ALD solution exists to deposit metal boride films at low temperatures. As a result, a method using ALD to form metal boride films is desired.
Further, a method for forming a metal boride film that attains desired dielectric constants as well as demonstrates reliability is desired.